1. Field of the Invention
This invention relates to metallization for the interconnection of semiconductor devices on a substrate and more particularly to such metallization which includes a low percent copper content aluminum/copper conductor.
2. Description of Related Art
Thin narrow interconnections have been used for some years for device interconnection purposes in the semiconductor integrated circuit industry. It is predicted that performance of these devices in the future will be limited by the performance of the device interconnection at the submicron level. At the submicron level, various technical problems are known to occur. While aluminum has been the preferred interconnection metal, as device dimensions are scaled down and current density increases, pure aluminum has been known to be susceptible to the problems of electromigration and hillock growth. To overcome the problems experienced with pure aluminum, aluminum has been alloyed with copper to form aluminum-copper. However, high percentage aluminum-copper (&gt;2%) is known to be difficult to dry etch and corrodes easily.
In an effort to improve on the use of aluminum-copper as the interconnection metallurgy, aluminum-copper has been taught to be layered with a refractory metal (i.e., U.S. Pat. No. 4,017,890). This patent teaches a method and resulting structure for forming narrow intermetallic stripes which carry high currents on bodies such as semiconductors, integrated circuits, etc., wherein the conductive stripe includes aluminum or aluminum-copper with at least one transition metal. While the aluminum-copper and transition metal structure has been known to improve the electromigration problems associated with aluminum-copper, the problems of etching and corrosion, as well as, the complete elimination of hillocks have not been solved.
As known in the art, hillocks are known to result from the large differences between the thermal expansion coefficients of the metal interconnect lines and the substrate creating compressive stresses in the metal. To eliminate and minimize hillock formation, it has been known in the art to use a multilayered structure instead of a single layer of the interconnect metallurgy. An effective reduction in hillock formation has been found to be achieved by using a multilayered structure of aluminum or aluminum intermetallic with a layer of refractory metal. Wherefore, a typical interconnect metallurgy structure would comprise a layered structure of aluminum silicon compound onto which there has been deposited, a layer of refractory metal, such as, titanium (see article "Homogeneous and Layered Films of Aluminum/Silicon with Titanium For Multilevel Interconnects", 1988 IEEE, V-MIC Conference, Jun. 25-26, 1985).
There have also been refinements to this layered metal structure to provide a lower resistivity, hillock free, interconnect metallurgy. These refinements include the incorporation of a barrier metal of, for example, titanium tungsten or titanium nitride under the aluminum silicon to prevent contact spiking and prevent the formation of ternary compounds in the aluminum silicon alloy (see article "Multilayerd Interconnections For VLSI" MRS Symposia Proceedings, Fall, 1987).
In addition, in this area, there have also been other proposed device interconnect structures to reduce resistivity and provide a more planar and defect free interconnect structure.
For example, IBM Technical Disclosure Bulletin, Vol. 21, No. 11, April, 1979, pp. 4527-4528, teaches the enhancement of the metallurgy for the interconnection due to sputtered deposition. Moreover, the feature of using a capping layer to improve performance has been proposed in IBM TDB Vol. 17, No. 1A, 1984 and TDB Vol. 21, No. 2, July 1978. However, no structure has been discovered which can satisfy all performance criteria providing a low resistance, hillock free, corrosion resistant, etchable, interconnection metallurgy structure.
It is, therefore, an object of the present invention to provide low weight percent copper (&lt;2%) content aluminum/copper conductor for device interconnection on a substrate with superior electromigration characteristics.
It is a still further object of the present invention to develop a multilayered interconnect metallurgy structure that is hillock free, dry etchable and corrosion resistant.
It is another object of the present invention to provide a multilayered interconnect metallurgy structure which has a low resistivity.